1. Field of the Invention
This invention relates generally to fiber delivery of ultra-short pulses, and more particularly to the use of photonic crystal fibers in an ultra-short pulse delivery system.
2. Description of Related Art
Fiber delivery systems are desirable for laser systems to provide convenient delivery of an output beam to a target distanced from the source. In particular, for ultra-short pulse lasers, a limiting factor in fiber delivery is the dispersion of the optical fiber.
At wavelengths of less than 1.27 microns, all step-index fibers have normal dispersion. In this regime, the ultra-short pulses broaden substantially while propagating in a fiber of lengths as short as a few meters. Prism or grating pairs, which provide anomalous dispersion, have been used to compensate the dispersion of the fiber. However, this increases complexity and cost and in the case of grating pairs, is inefficient. Additionally, with a tunable laser, the prism or grating pair requires adjustment as the wavelength is tuned.
There have been suggestions to use photonic crystal fibers to shift the zero dispersion wavelength to shorter values. In "Group-velocity dispersion in photonic crystal fibers", by D. Mogilevtsev, T. A. Birks and P. St. J. Russell, in Optics Letters 23, 1662 (1998) it is suggested that this may be useful in telecommunication systems. In "Efficient visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm", by J. K. Ranka, R. S. Windeler and A. J. Stentz, Postdeadline paper at CLEO 1999 (Optical Society of America), it is shown that in combination with a Ti:sapphire laser, novel non-linear effects are possible.
There is a need for a fiber delivery system for delivering ultra-short laser pulses. As a result, there is a need for a fiber that has an appropriate value of dispersion at wavelengths where common ultra-short pulse lasers operate.